To meet the demand for wireless data traffic having increased since deployment of fourth generation (4G) communication systems, efforts have been made to develop an improved fifth generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post long term evolution (LTE) System’. The 5G communication system is considered to be implemented in higher frequency millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing information technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies, such as a sensor network, MTC, and M2M communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud radio access network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
In order to support transmission of downlink and uplink transmission channels in a wireless communication system, related downlink control information (DCI) is necessary. In LTE in the related art, DCI is transmitted through a physical downlink control channel (PDCCH) that is a separate physical channel for transmitting the DCI, and the PDCCH is transmitted for each subframe over the whole system band.
Since one PDCCH carries one DCI message and a plurality of terminals may be simultaneously scheduled in downlink and uplink, transmission through a plurality of PDCCHs may be simultaneously performed in each cell. As a reference signal (RS) for decoding the PDCCH, a cell-specific reference signal (CRS) that is a cell-common reference signal is used. The CRS is an always-on signal transmitted for each subframe over the full band, and scrambling and resource mapping differ in accordance with a cell identity (ID). All terminals monitoring the PDCCH estimate channels using the CRS, and perform decoding of the PDCCH.
The CRS is a reference signal that is transmitted to all terminals in a broadcasting method, and thus, UE-specific beamforming is unable to be used. Accordingly, a multi-antenna transmission technique for the PDCCH of the LTE is limited to the open-loop transmission diversity.
As various technologies, such as carrier aggregation (CA) and coordinated multipoint (COMP), are supported in the LTE in the related art, it becomes difficult to secure sufficient transmission capacity for transmitting a downlink control signal only through the existing PDCCH being used.
Accordingly, in LTE Release 11, an enhanced PDCCH (EPDCCH) has been added as a physical channel for transmitting the DCI. The EPDCCH has been designed in a direction to satisfy the requirements, such as control channel transmission capacity increase, frequency-axis adjacent cell interference control, frequency-selective scheduling, and coexistence with the existing LTE terminals.
Since a demodulation reference signal (DMRS) that is a UE-specific reference signal is used as a reference signal for decoding the EPDCCH, the UE-specific beamforming can be used for the EPDCCH. Accordingly, the EPDCCH supports the multi-antenna transmission technique using precoding, and supports a transmission diversity technique using precoder cycling and a multiuser MIMO (MU-MIMO) transmission technique in accordance with a resource allocation method.
The downlink control channel as described above may have various formats, and the format of the downlink control channel is not pre-known to a terminal. Further, since the downlink control channel can be transmitted from a certain resource in a set of time/frequency resources defined as a search space, an accurate time/frequency resource for transmitting the downlink control channel is not pre-known to the terminal. Accordingly, decoding of the downlink control channel in the terminal is based on blind decoding.
For example, the blind decoding means that a terminal performs decoding of the downlink control channel with respect to combinations of all possible downlink control channel formats and all possible time/frequency resources in a given search space.
In LTE, the downlink control channel may be transmitted at each subframe interval, and thus, the terminal should perform monitoring of the downlink control channel for each subframe, that is, blind decoding. As an example, with respect to an LTE PDCCH, the terminal may perform blind decoding of the downlink control channel maximally 44 times for one component carrier.
The blind decoding as described above imposes a great burden from the viewpoint of power consumption of a terminal. Accordingly, there is a need for a new technique for monitoring a downlink control channel in order to reduce power consumption of the terminal due to the blind decoding of the downlink control channel.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.